address and explain the following questions 1 List some prac

address and explain the following questions:

1. List some practical consideration of strain measurement using strain gage

2. Discuss how to calibrate strain gage (Please refer to the article attached under :Shunt Calibration of Strain Gage Instrumentation)

Link:

http://www.vishaypg.com/docs/11064/tn514.pdf

Solution

Practical Considerations of strain measurement using strain gage:

Thermal Heating:On a practical note, an experimentalist dealing with the very real-world issues of measurement uncertainties and signal-to-noise ratios might conclude from the equation

Vmeas=Vin[1/4Rg,o]Rg,oGF

that one should use the largest excitation voltage, Vin, possible in order to produce the largest measured voltages possible, thereby maximizing measurement sensitivity.

But there is a practical consideration that limits Vin. It is that large voltages, which naturally lead to large currents, can produce high heat generation rates .

In this case, high heat generation rates can cause problems for the electronics in the data acquisition system. Specifically, as things heat up, they expand.

The key consequence is that the resistance of the strain gauges in the Wheatstone Bridge circuit can and will change.

This is obviously bad because it leads to nonzero Vmeas even though =0. Worse, the heat generated by the strain gauge can pass into the object it is attached to and heat it, causing it to expand. This will show up as measured strain, even though it is not caused by any loads.

This can be worse in composites than in metals because metals are usually good heat conductors and can therefore conduct the heat generated in the strain gauge away with minimal temperature rise.

Shunt Calibration of Strain Gage:

Shunt Calibration is a technique for simulating strain in a piezo-resistive strain gage Wheatstone bridge circuit by shunting one leg of the bridge.

The bridge may be internal to a discreet transducer or composed of separately applied strain gages. The resulting bridge output is useful for calibrating or scaling instrumentation.

Such instrumentation includes digital indicators, amplifiers, signal conditioners, A/D converters, PLC’s, and data acquisition equipment.